Rocket motors employing solid propellant generally have a rigid outer casing or shell (case), a liner layer bonded to the insulating layer and a solid propellant grain bonded to the liner. In general, case bonded solid propellant grains possess greater strength because of the additional support given by their adherence to the rocket motor casing in which they are contained. To insure the maximum strength and to prevent separation of the propellant grain from the motor walls which would create voids and therefore a potential for uneven burning, it is desirable that the propellant grain be bonded to the motor casing uniformly and firmly.
This is usually accomplished by very careful cleaning and descaling of the inside surface of the metal motor case, applying and vulcanizing an elastomeric insulator, followed by coating the inside surface with a liner, normally the binder used for the propellant grain, then casting the liquid propellant in place and curing into the final grain form. The liner serves as a bonding agent between the case and the propellant grain, as an inhibitor preventing burning down the outer surface of the grain and as an insulator, protecting the case from the heat and gases of combustion when burning has progressed to the point at which the case would otherwise be exposed.
U.S. Pat No. 4,429,634 of J. Byrd and J. Hightower, issued Feb. 7, 1984 to Thiokol Corporation, discloses a typical means of providing such a liner for bonding a solid propellant grain to a rocket motor casing employing an aziridine in a polyisocyanate cured hydroxyl-terminated polybutadiene based liner. Similarly, in U.S. Pat. No. 4,601,862 of J. Byrd and R. Davis, issued July 22, 1986 to Morton Thiokol, Inc., there is disclosed a process for providing a delayed quick cure rocket motor liner for binding a solid propellant grain to a rocket motor casing by utilizing a hydroxyl-terminated polybutadiene prepolymer, a polyisocyanate curing agent for curing said prepolymer by forming urethane linkages, a trifunctional aziridine adhesion promoter, filler and a curing catalyst comprising maleic anhydride, magnesium oxide and triphenyl bismuth.
However, it would be preferable if one were not restricted in the manufacturing process by the "potlife" of liner formulation, and if one could rapidly cure the liner mixture in the case. The state of the art prior art materials described above have a working potlife of typically about 1 to 12 hours once the isocyanate and hydroxy terminated prepolymer are mixed, and required from about 4 to 48 hours curing time in heated (63.degree. C. to 77.degree. C.) ovens. Potlife is defined as the amount of time a liner formulation is liquid enough to be spray or sling applied. It is also desirable that a ready and easy means be available for curing the liner composition, such as by radiation, e.g. UV radiation from sunlight, and that additional curing agents for curing the liner or the hydroxyl-terminated polybutadiene prepolymer not be required. A further objective of the invention would be to provide a rocket motor case liner that itself bonds to the solid propellant thereby improving liner/propellant adhesion.